This invention relates to a spring balancer for pivotable cover lid having a heavy weight which opens or closes upward and downward around horizontal axis (hereafter merely called "spring balancer").
The moment of revolution of the lid secured rotatively in upper and lower directions to a fixed body through a horizontal axis changes according to the change of a revolution angle of the lid. A balancer of this invention is attached between said lid and the fixed body and adapted to act a resistant force against a gravity direction on the lid, thereby preventing an impact rotation of the lid or enabling the stop of the lid at an arbitrary rotation angle.
As an example for operating such heavy lid which opens or closes in both upper and lower directions around the horizontal axis, there is an office machine, for instance, a copy apparatus.
Heretofore, since the lid which is opened or closed at the times of inspection and maintenance is heavy, a hinge wherein a torsion spring or the like energizes said lid in the opening direction is used close by the rotation axis in order to decrease the operation force.
In this case, however, a wide space is not only required for attaching the spring near the horizontal axis, but it is also difficult to design the spring characteristics to agree with the change of the moment of revolution of the lid. Therefore, the above spring has such a defect as changing the opening or closing action of the lid into an impact motion or a difficulty to stop the lid at an arbitrary position within the range of a full process in opening and closing.
Further, there exists a balancer wherein a compression coil spring is incorporated therein other than the above hinge. Such a balancer, however, has such defect as causing a wearing damage by the contact of the compression coil spring with other structural member made of metal at the time of the action of the balancer or an occurrence of a creaky noise by this contact.
Various kinds of invention have been performed in order to remove these defects mentioned above. For instance, such invention as coating the compression coil spring with a grease or the like, or forming the structural member other than the compression coil spring with a synthetic resin material, has been performed. However, the former is only a temporary means of a solution wherein a troublesome operation such as recoating of the grease is requested, and in the latter a new problem such as the deterioration of the mechanical strength of the balancer occurs since it is made of synthetic resin. Therefore, these are not practical means of solution for removing the defect of the compression coil spring.
Further, in case of no employment of the hinge or the balancer described above, there exists such one wherein a gas spring or an oil spring is laid between the lid and the body at a position spaced from the horizontal axis. In these balancer, though it is comparatively easy to agree its properties with the moment of the revolution of the lid, the cost becomes high because of the necessity of a sealing technique for prevention of the gas or the oil leakage, and further a complete maintenance of the sealing for a long period is also impossible. Accordingly, since the gas or oil leakage occurs by all means, the reliability as the balancer is low.
Furthermore, since the both of the gas and oil springs change the properties respectively according to the change of a temperature, these springs have such defects as difficulty in maintaining the performance of balancer always constant.
Accoringly, this invention is performed with the object of amending these defect.